MADEIRAN GROUP. 125 



( Spirorbula, Lowe.) 



Helix obtecta. 



Helix obtecta, Lowe, Cambr. Phil. S. Trans, iv. 47. t. 5. 



f. 20 (1831) 



Pfeiff, Mon. Hel. i. 188 (1848) 



Lowe, Proc. Zool. Soc. Land. 175 (1854) 



Alb., Mai. Mad. 34. t. 8. f. 20-22 (1854) 



Paiva, Mon. Moll. Mad. 60 (1867) 



Habitat Portum Sanctum ; et recens et semifossilis, prse- 

 sertim in aridis apricis calcareis, vulgatissima. 



The H. obtecta, Lowe, is peculiar to Porto Santo and the 

 immediately adjacent rocks, where it is one of the most 

 abundant and universal of the Helices, occurring more espe- 

 cially in the driest and most calcareous spots ; and it is almost 

 equally common in a subfossil condition. On the summit of 

 the Ilheo de Baixo it swarms ; and from its habit of coating 

 itself with a hard covering (strongly cemented together) either 

 of earth or of calcareous sand, it has often a very remarkable 

 and misshapen appearance. 



The flattened spire and almost concave apex of the H. ob- 

 tecta, the whorls of which are nevertheless raised and tumid, 

 with the suture deeply impressed, added to its rough, uneven 

 (though minutely and obsoletely granulated), and opake surface, 

 its dingy-brown hue, its rounded aperture and elevated, con- 

 tinuous peristome, and its appreciably keeled or subangulated 

 basal volution (which is also obscurely eroded, or subconcave, 

 immediately above the keel), will sufficiently distinguish it. 



Helix latens, 



Helix latens, Lowe, Ann. Nat. Hist, ix (1852) 

 Pfeiff., Mon. Hel. iii. 115 (1853) 

 Lowe, Proc. Zool. Soc. Lond. 175 (1854) 

 Alb., Mai. Mad. 34. t. 8. f. 23-26 (1854) 

 Paiva, Mon. Moll. Mad. 59 (1867) 

 Habitat Maderam ; inter detritus radicesque plantarum ad 

 basin rupium in humidis editoribus sylvaticis praecipue degens, 

 rarior. 



Although diametrically opposed to it in the extreme thin- 

 ness and fragility of its substance (which, as regards texture, is 

 almost membranaceous), the present Helix may nevertheless be 

 regarded as the Madeiran representative of the H. obtecta of 

 Porto Santo. And indeed in their general outline and some- 

 what Planorbis like contour (the nucleus of both being so 



